|M.Sc Student||Ilia Meerovich|
|Subject||Denitrification of Brines in an Upflow Sludge Blanket (USB)|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Green Michal|
|Full Thesis text - in Hebrew|
This research work investigated the biological removal of nitrate from waste brines created in membrane treatment processes. An USB reactor is a biofilm reactor characterized by a self-agglomerating granular biomass that has no carrier. Based on previous results with groundwater denitrification, the hypothesis of this research was that positive precipitation potential with the corresponding increase in the mineral fraction of the biomass, is a prerequisite to an efficient operation of brine denitrification reactor, due to its effect on biomass settling characteristics. In order to verify this hypothesis two different carbon sources were studied: acetic acid which results in a precipitation potential close to zero, and ethanol which results in a positive precipitation potential . The influence of ethanol and acetic acid as electron donors was examined in two identical reactors. Nitrate concentration in influent was 120 mg N-NO3/liter and the VSS to TSS ratio was 0.22 in the sludge used as inoculum. In the experiment lasting 120 days, the efficiency of nitrate reduction in the reactor that was fed with ethanol was high (above 95 %), but stable only at low loads (up to about 4 gram N/liter). At higher loads, channeling was evident and effluent quality deteriorated. The sludge in the ethanol fed reactor contained a high mineral fraction (80% of TSS) and a very low SVI value of 4 ml/g sludge. Nitrate reduction efficiency in the acetic acid fed reactor was higher then 95% and the concentration of total nitrogen in the effluent was lower then 5 mg/liter. Instability in the reactor with acetic acid as electron donor appeared only at loads higher then 10 gram N/day. In the acetic acid fed reactor, a sharp increase was seen in the biomass VSS to TSS ratio (0.9) due to a decrease in the reactor precipitation potential. Despite the decrease in mineral fraction that was followed by an increase in SVI, SVI values were still very low (less then 20 ml/g). The results showed that high efficient denitrification of brine and good biomass settling characteristics are not affected by the biomass mineral content. It is possible that the higher ionic strength in the brine reactor (NaCl 1%) affects the settling characteristic of granules.